1. Field of the Invention
This invention relates to a line switching apparatus and method for performing line connection between an extension and a telephone line.
2. Description of the Prior Art
Conventionally, with an apparatus of this type, such as a private branch exchange (hereinafter referred to as a "PBX") or key telephone system (hereinafter referred to as a "KTS"), so-called telephone line camp-on (or trunk cueing) is available as a service function for an extension when all telephone lines are being used. Also available is so-called extension camp-on which, when a call is to be placed on an extension, is a service function for the extension used if the extension of the other party is busy.
These service functions will now be described taking the PBX as an example.
First, in telephone line camp-on, the extension telephone is taken off the hook and "0" is dialed in order to call a telephone line. If the telephone line trunks are all busy at this time, the PBX sends a busy tone (BT) to the extension telephone. When the operator of the extension hears the BT, the operator dials a special number (a specific number) for the telephone line camp-on service and then hangs up upon confirming an intercept tone from the PBX indicating the completion of registration. When a telephone line trunk subsequently becomes available, the PBX calls the extension and the operator takes the extension telephone off the hook. When this is done, connection to the telephone line trunk is achieved.
Next, in extension camp-on, the extension telephone is taken off the hook and an extension number is dialed in order to communicate with another party's extension. If the other party's extension is busy at this time, the PBX sends the BT to the extension telephone. When the operator of the extension hears the BT, the operator dials a special number for the extension camp-on service and then hangs up upon confirming an intercept tone from the PBX indicating the completion of registration. When the busy extension subsequently becomes available, the PBX calls the registered extension telephone and the operator takes the extension telephone off the hook. When this is done, the other party's extension is called. When a response is received owing to the other party's extension being taken off the hook, connection to the other party's extension is achieved.
In the examples described above, several seconds and, in some cases, ten seconds or more are required for camp-on registration to be completed. This leads to the following disadvantages:
(1) Even if a telephone line trunk becomes available during camp-on registration, the extension being registered is made to wait if the telephone line is called (i.e., if "0" is dialed) from another extension during registration, or if the other party's extension ends communication and is taken off the hook in order to make a call.
(2) Similarly, if there is an incoming call to an available telephone line trunk from a telephone line, or if there is an incoming call to the other party's extension which has terminated a conversation, the abovementioned calling extension is made to wait.
Thus, as set forth above, there are cases where a user who has registered camp-on in order to use a telephone line trunk quickly or to rapidly communicate with another party's extension is in the end made to wait. This is highly inconvenient.
In addition, operability is poor in that even if a line becomes free during the registration operation, the user must wait until camp-on registration is completed and the call tone is issued.
Furthermore, even when a telephone line trunk becomes free and the registered extension is called after telephone line camp-on registration in the above-described example, several seconds are required until a response is received from this extension. If there is no response to the call, the telephone line trunk that is free cannot be used.